Rees-Mogg said May ‘ought not to take Brussels too seriously about the Irish question’.
Photograph: Matt Cardy/Getty Images

Theresa May’s inner Brexit cabinet is preparing to meet again, with ministers pessimistic about breaking the customs deadlock after Jacob Rees-Mogg said hard Brexit MPs would not back down.

Ahead of the subcommittee meeting on Tuesday, Rees-Mogg, who heads the European Research Group of pro-Brexit Conservative MPs, said he was not minded to take a more conciliatory position. “If we were to do so it would completely undermine the heart of why we voted to leave, rendering our almost-reclaimed sovereignty a myth,” he said.

He repeated calls for Britain to walk away from the negotiations if the options May gave the European commission were rejected. “The UK will simply have to leave with no deal because the referendum result must be upheld,” he said. “Democracy is the backbone of established political societies, it fosters stability and fairness and cannot be treated so disdainfully.”

Writing in the Daily Telegraph, Rees-Mogg said May “ought not to take Brussels too seriously about the Irish question” when seeking a customs deal.

“The commission hides behind faux concern for the Irish border undermining the single market ... We will not impose a border. If there is a deal to be done about the border it will be precisely that: a deal. Nonetheless, if one side keeps refusing to bargain, no deal will be struck.”

The intervention came after May held private meetings with dozens of Conservative backbench MPs to try to explain the two options for customs arrangements with the EU. She and Rees-Mogg are reported to have clashed over the consequences for the Irish border during their meeting.

The inner Brexit cabinet meets again on Tuesday afternoon to discuss the two rival plans. May still faces having to deal with a significant split among ministers over whether to back a customs partnership, where the UK would collect tariffs on behalf of the EU, or opt for the “max fac” model, which would use technology to police the border.

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Conservative MPs were invited to five separate sessions at the Department for Exiting the European Union, where May made introductory remarks and took questions. Her chief of staff, Gavin Barwell, then gave a “neutral, technical” presentation of both options, with MPs given the chance to press him further on the detail afterwards. A Brexiter source said the presentation had been “neutral to the point of being incoherent”.

David Mundell, the Scottish secretary, said the cabinet would “test proposals to destruction” and denied the arguments were coming too late in the process.

“We’ve been very focused on other aspects of Brexit, agreeing the withdrawal agreement, the implementation period. The EU themselves set a timescale to discuss these issues and it’s right that we’re focusing on it now,” he told BBC Radio 4’s Today programme.

“We are focusing on it in a way that ensures that we get it right, that we test proposals to destruction.” Asked if that phrasing meant he agreed with Boris Johnson’s assessment that the customs partnership was “crazy”, Mundell said: “I agree with cabinet collective responsibility, we’ll look in detail at proposals that have been worked through by the sub-committees.”

Before the full Brexit subcommittee meeting on Tuesday, May also faced pressure from the former John Lewis boss Andy Street, who won the West Midlands mayoralty in a surprise win over Labour last year.

Street, a Tory remainer, said his region’s car industry was facing an uncertain future without a comprehensive customs deal. His remarks echo those made last week by the business secretary, Greg Clark, who favours the customs partnership option.

“As the cabinet examines the different systems for administering customs after Brexit, it must ensure that whatever the final arrangements are, they sustain the manufacturing renaissance we have seen in the West Midlands,” Street wrote in the Times.

He said technology would be “part of the solution” but said trade flow was crucial. “If the technology doesn’t work for car parts at Dover or Felixstowe, if there are big delays, new checks or burdensome processes to claim back customs paid, costs will go up and companies will struggle,” he said.

“If we get this wrong, we will see the unintended destruction of thousands of jobs in the automotive industry in the West Midlands.”